Chapter 1 Databases and Database Users

Copyright © 2011 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

Chapter 1

Databases and

Database Users

Copyright © 2011 Ramez Elmasri and Shamkant Navathe

Introduction

Database Collection of related data

• Known facts that can be recorded and that have implicit meaning

Implicit properties:• Represents some aspect of the real world:

Miniworld or universe of discourse (UoD)• Logically coherent collection of data with inherent

meaning• Built for a specific purpose


Database management system (DBMS)

Database management system (DBMS): Collection of programs Enables users to create and maintain a database;

Defining a database: Specify the data types, structures, and constraints of the data to be stored

• Meta-data: Database definition or descriptive information; Stored by the DBMS in the form of a database catalog or dictionary

Constructing: storing the data on some storage medium Manipulating a database

• Query and update the database miniworld • Generate reports

Sharing a database • Allow multiple users and programs to access the database simultaneously

Application program: Accesses database by sending queries to DBMS• Query: Causes some data to be retrieved• Transaction: May cause some data to be read and some data to be written into the database

Protection includes: • System protection: against hardware or software malfunction• Security protection: against unauthorized or malicious access

Maintain the database system • Allow the system to evolve as requirements change over time

Database + DBMS = database system



An Example

UNIVERSITY database Information concerning students, courses, and

grades in a university environment

Data records STUDENT COURSE SECTION GRADE_REPORT PREREQUISITE



An Example (cont'd.) Specify structure of records of each file by specifying data type for each data element

String of alphabetic characters Integer Etc.

Construct UNIVERSITY database Store data to represent each student, course, section, grade report, and prerequisite as a record in

appropriate file

Relationships among the records Records in STUDENT file is related to records in GRADE_REPORT

Manipulation involves querying and updating Examples of queries:

• Retrieve the transcript

• List the names of students who took the section of the ‘Database’ course offered in fall 2008 and their grades in that section

• List the prerequisites of the ‘Database’ course

Examples of updates:• Change the class of ‘Smith’ to sophomore

• Create a new section for the ‘Database’ course for this semester

• Enter a grade of ‘A’ for ‘Smith’ in the ‘Database’ section of last semester


An Example (cont'd.)

Phases for designing a database: Requirements specification and analysis Conceptual design Logical design Physical design


Characteristics of the Database Approach

File vs. database Traditional file processing

• Each user defines and implements the files needed for a specific software application –duplicate efforts

• Waste storage space and in redundant efforts to maintain common up to date data

• Data may become inconsistent

Database approach: Single repository maintains data that is defined once and then accessed by various users


Characteristics of the Database Approach (cont'd.)

Self-Describing Nature of a Database System Database system contains complete definition of

structure and constraints• Meta-data: information stored in the catalog

Describes structure of the database

Database catalog used by: • DBMS software • Database users who need information about database

structure




Insulation Between Programs and Data Program-data independence

• Structure of data files is stored in DBMS catalog separately from access programs• Program-operation independence

Operations specified in two parts:• Interface includes operation name and data types of its arguments • Implementation can be changed without affecting the interface

Data Abstraction: Allows program-data independence and program-operation independence

• DBMS provide Conceptual representation of data• Does not include details of how data is stored or how operations are implemented

• Data model is Type of data abstraction used to provide conceptual representation• Data model uses logical concepts, such as objects, their properties and their relationships • Data model hides storage and implementation details that are not of interest to most

database users




Support of Multiple Views of the Data View

• Subset of the database • Contains virtual data derived from the database

files but is not explicitly stored

Multiuser DBMS • Users have a variety of distinct applications• Must provide facilities for defining multiple views




Sharing of Data and Multiuser Transaction Processing Allow multiple users to access the database at the same time Concurrency control software

• Ensure that several users trying to update the same data do so in a controlled manner

• Result of the updates is correct Online transaction processing (OLTP) application

• Multiple agents access to flight ticket for reservation Transaction: is an executing program or process that includes one

or more database accesses.• Central to many database applications• Executing program or process that includes one or more database• Transaction properties:

• Isolation property: Each transaction appears to execute in isolation from other transactions

• Atomicity property: Either all the database operations in a transaction are executed or none are


Actors on the Scene Database administrators (DBA) are responsible for:

Authorizing access to the database Coordinating and monitoring its use Acquiring software and hardware resources

Database designers are responsible for: Identifying the data to be stored Choosing appropriate structures to represent and store this data

System analysts: Determine requirements of end users, and develop specifications fro standard canned transactions that meet these requirements.

Application programmers: Implement these specifications as programs. End users: People whose jobs require access to the database

Casual end users Naive or parametric end users

• Reservation agents; bank teller Sophisticated end users Standalone users


Workers behind the Scene

DBMS system designers and implementers Design and implement the DBMS modules and

interfaces as a software package

Tool developers Design and implement tools

Operators and maintenance personnel Responsible for running and maintenance of

hardware and software environment for database system


Advantages of Using the DBMS Approach

Controlling redundancy Redundancy: storing data multiple times:

• Redundancy is controlled when the DBMS ensures that multiple copies of the same data are consistent

• If the DBMS has no control over this, we have uncontrolled redundancy.

Data normalization: store each logical data item in only one place

Denormalization: Sometimes necessary to use controlled redundancy to improve the performance of queries



Advantages of Using the DBMS Approach

Restricting unauthorized access Security and authorization subsystem Privileged software

Providing persistent storage for program objects Complex object in C++ can be stored

permanently in an object-oriented DBMS Impedance mismatch problem

• Object-oriented database systems typically offer data structure compatibility


Advantages of Using the DBMS Approach (cont'd.)

Providing storage structures and search techniques for efficient query processing Indexes Buffering and caching Query processing and optimization

Providing backup and recovery Backup and recovery subsystem of the DBMS is

responsible for recovery Providing multiple user interfaces

Graphical user interfaces (GUIs) Representing complex relationships among data

May include numerous varieties of data that are interrelated in many ways



Enforcing integrity constraints Referential integrity constraint

• Every section record must be related to a course record

Key or uniqueness constraint• Every course record must have a unique value for

Course_number

Business rules Inherent rules of the data model



Permitting inferencing and actions using rules Deductive database systems

• Provide capabilities for defining deduction rules• Inference new information from the stored database facts

Trigger: a form of a rule activated by updates to the table, which results in performing additional operations to some other tables.

Stored procedures• More involved procedures to enforce rules

• Active database system: provide active rules that can automatically initiate actions when certain events and condition occur



Additional implications of using the database approach Potential for enforcing standards Reduced application development time Flexibility Availability of up-to-date information Economies of scale


A Brief History of Database Applications

Early database applications using hierarchical and network systems Large numbers of records of similar structure

Providing data abstraction and application flexibility with relational databases Separates physical storage of data from its

conceptual representation Provides a mathematical foundation for data

representation and querying


A Brief History of Database Applications (cont'd.)

Object-oriented applications and the need for more complex databases Used in specialized applications: engineering

design, multimedia publishing, and manufacturing systems

Interchanging data on the Web for e-commerce using XML Extended markup language (XML) primary

standard for interchanging data among various types of databases and Web pages


A Brief History of Database Applications (cont'd.)

Extending database capabilities for new applications Extensions to better support specialized

requirements for applications Enterprise resource planning (ERP) Customer relationship management (CRM)

Databases versus information retrieval Information retrieval (IR)

• Deals with books, manuscripts, and various forms of library-based articles


When Not to Use a DBMS

More desirable to use regular files for: Simple, well-defined database applications not

expected to change at all Stringent, real-time requirements that may not

be met because of DBMS overhead Embedded systems with limited storage

capacity No multiple-user access to data


Summary

Database Collection of related data (recorded facts)

DBMS Generalized software package for

implementing and maintaining a computerized database

Several categories of database users Database applications have evolved

Current trends: IR, Web, no-sql

Documents

Chapter 1 Databases and Database Users